Can you post a pic? Blue Stripe could be early ls6 springs or AFR had some single springs that had Blue stripe as well on a set I had a long time ago. Not sure of a actual purple stripe though. I've seen Yellow, Full Blue, Blue Stripe, Yellow Stripe, Pink and Green striped. Were they stock heads?
04 PBM M6 GTO - Pedders XA's/All Bushings/Ported 5.3L Heads/Ed Curtis Custom Cam/Kooks 1 7/8ths headers No cats/Magnaflow Exhaust/Volant CAI/4.10 Gears with Harrop Cover and Harrop LSD/G Force DS with Billet Yoke/42Lbs Injectors/Chrome 18's (OEM)/06 Brake Conversion/Limo Tint/Eclipse Nav system/HID Low and Fogs/SAP Front and Rear bumper/SAP Grills/Spoiler Delete